Prior patents DE-AS No. 2,126,258 and DE-AS No. 2,613,174 disclose devices for controlling grippers in sheet-fed rotary presses of the kind referred to above, wherein only one drive is provided to control the gripper shaft. If considerable gripper forces are applied, the system comprising the gripper control cam, cam follower, drive lever, gripper shaft and adjustment means may be distorted on closing due to overloading of the considerably pre-stressed grippers, so that the closing operation is delayed and the power build-up lengthened. As a result, even at high speeds the impact force of the grippers does not go beyond the static retaining force such that blurring results with considerable distortion of the system.
DE-PS No. 834,107 discloses a device for controlling grippers in sheet-fed rotary presses having two drives disposed in parallel relationship and jointly turning a torsion spring to produce an identical or a different stress condition, the drives being disposed on each side of an impression cylinder. This device relates to a pre-gripper control system and not the control of grippers of the rotating cylinder. However, it is not possible to adjust the gripper opening width, so that register differences occur.
The primary aim of the present invention is to enable power built up to close the grippers to be introduced symmetrically from a central point on the gripper shaft with the required accuracy via two parallel drives so as to be adjustable to different printing materials, in order to obviate register differences and blurring.
According to the invention the grippers are arranged in a row on the gripper shaft disposed on a rotating cylinder. The gripper shaft is centrally controlled between its ends by two cam control systems acting in parallel relationship on the ends of an actuating shaft, by turning of the latter, with a central adjusting means interconnecting the actuating shaft and the gripper shaft to provide a symmetrically divided torsional force adjustable to vary the opening width of the grippers according to the sheet thickness being processed. The actuating and gripper shafts may be disposed in spaced apart parallel relation or concentric to one another.
The advantages of the invention are that faster gripper closure and shortened power build-up are obtained, because distortion of the system comprising the gripper control cam, drive lever, cam follower, actuating shaft, gripper shaft and adjustment means is reduced despite increased gripper forces. The power is introduced centrally and symmetrically to both cam control systems so as to be adjustable to different printing materials, so that register differences and blurring are obviated.